Oh, Apple. Ohhh, Apple. Today's rookie mistake is a system process called writeconfig that, through a case of the infamous confused deputy problem (it exists to allow certain operations by System Preferences and its command line equivalent systemsetup to be performed by admin users that are not root), can be coerced to allow any user to create arbitrary files with arbitrary permissions -- including setuid -- as root. That's, to use the technical term, bad.
This problem exists in 10.10, and is fixed in 10.10.3, but Apple will not fix it for 10.9 (or 10.8, or 10.7; the reporters confirmed it as far back as 10.7.2), citing technical limitations. Thanks, Apple!
The key is a privileged process called writeconfig which can be tricked into writing files anywhere using a cross-process attack. You would ask, reasonably, why such a process would exist in the first place, and the apparent reason is to allow these later versions of systemsetup et al to create user-specific Apache webserver configurations for guest users. If systemsetup doesn't have this functionality in your version of Mac OS X, then this specific vulnerability, at least, does not exist.
Fortunately, 10.6 and earlier do not support this feature; for that matter, there's no ToolLiaison or WriteConfigClient Objective-C class to exploit either. In fact, systemsetup isn't even in /usr/sbin in non-Server versions of OS X prior to 10.5: it's actually in /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Support/, as a component of Apple Remote Desktop. I confirmed all this on my local 10.4 and 10.6 systems and was not able to replicate the issue with the given proof of concept or any reasonable variation thereof, so I am relieved to conclude that Power Macs and Snow Leopard do not appear to be vulnerable to this exploit. All your PowerPC-base systems are still belong to you.
Meanwhile, on the TenFourFox 38 front, IonPower is almost passing the first part of V8. Once I get Richards, DeltaBlue and Crypto working the rest of it should bust wide open. Speed numbers are right in line with what I'd expect based on comparison tests on my 2014 i7 MacBook Air. It's gonna be nice.